1. Field of the Invention
This invention pertains generally to configuration Read Only Memory (ROM) implementations. More particularly, the invention is a system and method for providing a dynamic configuration ROM using double image buffers for use with serial bus devices.
2. The Prior Art
In serial bus architecture, a “node” is an addressable entity (i.e., a logical entity with a unique address), which can be independently reset and identified. The address space provided by a node can be directly mapped to one or more “units”. A unit is a logical entity, such as a disk controller, which corresponds to unique I/O (input/output) driver software. On a multifunction node, for example, a processor and I/O interfaces could be different units on the same node.
Nodes can be “interconnected” using an appropriate physical topology suitable for use with the serial bus, such as a “backplane environment” and/or “cable environment”, for example. These environments are described in further detail in Institute of Electrical and Electronics Engineers (IEEE) Standard 1394-1995 “IEEE Standard for a High Performance Serial Bus” published Aug. 30, 1996 which is incorporated herein by reference. Interconnected nodes may reside in either environment without restriction.
Configuration ROM implementations are well known in the field of serial bus devices and provide the hardware and software specifications of a serial bus node and its associated units. For example in IEEE Standard 1394, two configuration ROM formats are supported: minimal and general. The minimal ROM format provides a 24-bit company identifier. The general ROM format provides additional information in a bus_info_block and a root_directory. Entries within the root_directory may provide information or may provide a pointer to another directory (root-dependent directory and/or unit_directory), which has the same structure as the root_directory. Entries within the root directory may also provide a pointer to a leaf, which contains information. The unit_directories contain information about the units associated with the node, such as their software version number and their location within the address space of the node, for example.
FIG. 1 shows a general ROM implementation format for IEEE Standard 1394. The ROM directory structure is a hierarchy of information blocks, where the blocks higher in the hierarchy point to the blocks beneath them. The location of the initial blocks (info_length, crc_length, rom_crc_value, bus_info_block, and root_directory) are fixed. The location of the other entries (unit_directories, root and unit leaves) varies according to each vendor, but are specified by entries within the root_directory or its associated directories.
In general, the bus_info_block provides specific information about the node. For example, the bus_info_block may indicate whether the node carries out isochronous data transfers. Additionally, the bus_info_block provides a node_vendor_id field, a chip_id_hi field, and a chip_id_lo field, among other things. Together, the node_vendor_id, chip_id_hi, and chip_id_lo fields form a 64-bit node unique identifier. Other node specific information may be provided in the root_directory and the root leaves of the ROM. Unit specific information is normally provided in the unit_directory and the unit leaves of the ROM. For example, the specification identification and the version number may be provided for a particular protocol in the unit_directory and the unit leaves. IEEE Standard 1394-1995 “IEEE Standard for a High Performance Serial Bus” published Aug. 30, 1996 describes the general ROM format and its associated blocks in further detail and is incorporated herein by reference.
The configuration ROM is “published” to other nodes on the bus. That is, nodes on the bus may access some known address space on any node to read or otherwise ascertain that node's configuration ROM information at any time. Certain nodes (management entities) that carry out the operation of “controlling” other nodes proactively ascertain the configuration ROM information contained in other devices on the bus.
Originally, configuration ROM implementations were intended to be static and unchanging. As such, the configuration ROM information image provided to the other nodes on the bus remains fixed during the operation of the node. However, it may be desirable to “scale” the capabilities of a node while the node is already operational. For example, a node may want to provide an additional protocol service or an additional unit device, for example. However, the addition of a protocol or a unit device, in the above example, would require modification of the configuration ROM in order to “publish” the availability of the new unit architecture represented by the added protocol or unit device. Similarly when an existing software service (a protocol service, for example) is removed from the node, the configuration ROM would need to be updated to publish the unavailability of the removed software service.
Traditionally, changing or modifying the configuration ROM while “active” and available to the other nodes on the bus may result in inconsistent configuration ROM data. This inconsistency may result when, for example, a node is reading the ROM while the ROM is being updated. The requesting node may read the incorrect rom_crc_value, for example, because unit directories and unit leaves are being added for the newly added unit architecture. Thus, it would be disadvantage to update or modify and active configuration ROM available to the other nodes on the bus.
In order to “scale” a node (i.e., add or remove a unit for the node) according to the prior art, the node would have to be unlinked from the serial bus. Once unlinked from the serial bus, the configuration ROM is unavailable to the other nodes. Updates can then be made to the configuration ROM of the unlinked node without the risk of publishing inconsistent ROM data to the other nodes, as described above. After ROM update, the node can then link back to the serial bus and republish the newly updated configuration ROM information.
Accordingly, there is a need for a system and method for providing a dynamic configuration ROM which may be updated while linked to the serial bus and without risk of providing inconsistent configuration ROM information to the other nodes on the bus. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
An object of the invention is to provide a system and method for providing a dynamic configuration ROM, which overcomes the deficiencies in the prior art.
Another object of the invention is to provide a system and method for providing a dynamic configuration ROM in a node device wherein the configuration ROM may be updated while the node is active and linked with other devices.
Another object of the invention is to provide a system and method for providing a dynamic configuration ROM in a node device, which provides double ROM image buffers, one of which is active and the other which is modifiable.
Another object of the invention is to provide a system and method for providing a dynamically modifiable configuration ROM in a node device, which provides services to publish the dynamically modifiable configuration ROM.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.